1. Field of the Invention
The present invention relates to a cover for a support, more particularly to a cover for an inflatable support such as a mattress or cushion for a human or animal body. The invention also relates to methods of making such a cover, and to inflatable supports, such as mattresses, having a plurality of inflatable supports and the cover.
2. Description of the Prior Art
The use of pressure-cycling air inflatable mattresses is well known for the reduction of bed sores, and is described, for example, in GB-A-1 595 417. The present applicants sell a range of these mattresses for this purpose, for example, the Airwave Plus.TM., in which a controller sequentially inflates and deflates a plurality of overlapping groups of air tubes extending transversely to the length of the mattress. In this manner, each air cell cyclically provides support of, and relief from pressure to, a patient's body.
The majority of such inflatable mattress systems use a cover to prevent the mattress becoming contaminated or damaged by body fluids, wound exudate or other spillages. A cover for a mattress of this type must allow for the inflation and deflation of the air cells. Thus, a traditional mattress sheet as used on a conventional mattress will not suffice. Covers for inflatable mattresses are presently box-like in shape, having a top sheet and side sheets. The design relies on there being sufficient material elasticity and looseness in the top sheet to allow full inflation of the cells during the appropriate part of the inflation--deflation cycle. However, this type of cover on an inflatable mattress may prevent the achievement of zero interface pressure between the patient and the mattress. During the inflation and deflation cycle, one group of cells is necessarily in the deflated state. This deflation stage should allow a period of zero pressure on the patient's body, thus helping to reduce bed sores. However, the material of a cover as described above does not conform closely to the shape of the air cells and may form a hammock shape between inflated and deflated cells, or between two adjacent inflated cells. As a result, a state of zero pressure is not achieved where the cells are deflated. Thus, an inflatable mattress using a cover of this type is suitable only for patients at medium or high risk of developing bed sores, but is not suitable for those at very high risk. As a result, the use of the active mattress system is limited by the design of the cover.
As an alternative, a sheet might be used to cover the mattress, which closely follows the undulating shape of the inflating and deflating cells. However, the sheet does not remain accurately located in relation to the mattress, and further results in untidy skirts around the sides of the mattress which are difficult to keep clean.
It is thus an aim of the present invention to overcome and ameliorate the above problems of the prior art.
Accordingly, in a first aspect the present invention provides a cover for a support having a plurality of inflatable cells, said cover comprising a top sheet and at least opposite side sheets to which the top sheet is attached at opposite edges along an attachment length, wherein the length of the top sheet attached to the side sheets at said attachment length is, in its laid-flat state, greater than the length of said side sheet attached to the top sheet at said attachment length.
By this arrangement, the present invention provides a cover having a top sheet which has a full ness or non-tightness even when the side sheets are taut, as when mounted on a mattress. The top sheet therefore can conform closely to the undulating top surface of the air cells and yet is positively located in relation to the support, whilst the side sheets can lie flat and tidily against the sides of the support.
Preferably the top sheet and the side sheets are attached substantially continuously e.g. by stitching, along the whole of said attachment length, but attachment may be somewhat intermittent. Preferably the length of the top sheet, when laid flat is at least 50%, more preferably at least 10% greater than that of the side sheets. These lengths are measured in the unstitched condition.
The length of the top sheet attachment length to the side sheets may be the length parallel to any edge of the top sheet, and preferably is the length extending in the direction perpendicular to the longitudinal direction of the tubular air cells of the support being covered. The length of the side sheet attached to the top sheet may be the length parallel to any edge of the side sheet, and preferably is the length extending in the direction perpendicular to the longitudinal direction of the tubular air cells of the support being covered.
Preferably, the increase in length of the top sheet attached to the side sheet at the attachment length is, in its laid flat state, approximately equal to the difference in length of the upper surface of the mattress between a hypothetical situation where all cells are in the deflated state and the maximally inflated state of the air cells at any one point during a cycle.
Preferably the cover also comprises end sheets, joined to the top sheets and side sheets to form an open box-like structure, such that for example, each end sheet is substantially perpendicular to the side sheets, and to the top sheet, when the cover is fitted to the support.
The cover may also comprise an outer skirt, which lies external and parallel to the side sheets, extending around at least a portion of the circumference, and preferably the entire circumference of the support. The outer skirt preferably covers any joint (such as a zip fastener described below) between a base portion and the side sheets, thus reducing risk of entry of fluids through the joint.
Preferably, the cover also comprises a base portion, which may be a flat sheet or more preferably an open box-like structure. The base portion may be releasably attached, e.g. by a zip fastener, to the side sheets attached to the top sheet, such that the individual components may be separately cleaned and replaced.
An internal strap system may also be provided within the cover, in order to secure the cover to the support. Preferably, the system consists of one or more straps attached by at least one end to the cover and comprising means for attachment to the support. Such means may be a hook. One or more such internal straps may be attached to external straps, which are used to secure the support and cover to an external member, such as a bed frame or chair. Preferably, the internal and external straps are joined to each other through the cover or are joined only to the cover, thereby ensuring that piercing of the cover is kept to a minimum to reduce possible ingress of liquids. Thus, stress caused by fixing a support to an external member is transferred through the internal and external strap system to the support itself, allowing the cover to remain substantially free of stress. The internal and external strap system may be adapted in accordance with user specific requirements.
At least one handle, and preferably a pair, may be provided on the external surface of the cover, in order to facilitate moving of the mattress. The handles may be located at any position on the cover, but preferably are on opposing side sheets or end sheets of the cover.
The handles may be integral with or attached to internal straps located within the cover. These internal straps may be the same or different from the straps of the internal strap system. They may be located at any position within the cover, corresponding to the position of the handles on the outer surface. Where the internal straps are attached also to the support, this system allows the support and cover to be moved while minimizing strain on the cover itself.
The support can be a device such as an air inflatable mattress for the prevention of bed sores, or a cushion for a wheel chair for a similar purpose, or a calf support attachable to a wheel chair, having a plurality of groups of inflatable air cells which inflate and deflate sequentially and extend in a transverse fashion across the surface of the support. There may be two or more layers of tubes as shown in GBA-1595417. Each group of cells has at least one cell, preferably two or more, depending on the size of the support.
The inflatable cells of the support may be of any shape, but it is preferable that they are tubular in shape and lie transverse to a longitudinal direction of the support.
In a second aspect of the present invention there is provided a method of making a cover for a support having a plurality of inflatable cells, said cover comprising a top sheet and side sheets to which the top sheet is attached along opposing edges, wherein the method comprises the following steps:
(i) stretching said side sheets along their length, and PA1 (ii) joining the side sheets in their stretched condition to the top sheet when the top sheet is unstretched or is stretched to a lesser extent than the side sheets, so that when the side sheets are relaxed, they cause the top sheet to assume a length which is less than its laid flat length.
The side sheets may be stretched along whole or part of their length, or sequentially along different parts of their length.
The length of the top sheet attachment length to the side sheets, and the length of the side sheets, may be as described above.
The increase in length of the top sheet attached to the side sheet at the attachment length may also be as described above. A small amount of stretching of the top sheet during this process may prevent puckering of the material during joining.
The process described above may be performed on parallel edges of the top sheet, preferably said edges extending in the direction of the attachment length as described above. In order to prevent puckering or "creep" of the material, it is preferable that the joining is carried out in the same direction along the parallel edges of the top sheet.
Joining the side sheets to the top sheets may be done in one or more steps. Preferably, the side sheets are first attached to the top sheet at one or more points spaced apart along the attachment length. Preferably, the side sheets are first attached to the top sheet at the ends of the attachment length. Such attachment prior to the joining process allows accurate alignment of the top sheet and side sheet in relation to one another, such that the top sheet displays no twist or misalignment across the inflatable cells of a support, when placed on a support. The side sheets and top sheets are then stretched and joined together between said points. The side sheet and the top sheet may then be relaxed from their stretched condition.
It is preferable also that an outer skirt sheet is provided, external to and parallel to the side sheets. Preferably the outer skirt extends around the entire circumference of the cover. If an outer skirt is used, the outer skirt and side sheets may be joined to the top sheet simultaneously, according to the method described above. This prevents the need for additional joints in the cover.
The side sheets and outer skirts may be joined to the top sheet by any conventional joining method, such as gluing, heat sealing or stitching. Preferably, stitching is used. The stitching may be of any suitable type, but may be a machine stitch, e.g. of approximately 12 stitches per inch. Such a pitch allows a tight join between the materials, preventing puckering and gathering, and still allowing said materials to return to their unstretched condition.
Prior to stretching and joining the side sheets and end sheets to the top sheet, one half of a zip fastener may be joined to the side sheets and end sheets. One edge of the outer skirt may be tape sealed, prior to joining to the top sheet.
Alternatively, the zip fastener portion and tape sealing may be added to the side sheets and outer skirt after stretching and joining to the top sheet.
End sheets may also be joined to the top sheet, such that when the cover is fitted to a support each end sheet is approximately perpendicular to the side sheet and to the top sheet. The end sheets may be joined prior to, or after, joining and relaxing of the side sheets and the outer skirt. The side sheets and outer skirts may then be everted together with the end sheets to form a box-like structure.
After relaxation of all components to their unstretched condition, one or more outer joints may be added to the outer surface of the cover, joining all components of the cover, in order to hold the components together more securely. Preferably, a single outer joint is made around the entire circumference of the cover. The outer joint may use any conventional technique, such as stapling, rivetting or stitching. Preferably, stitching is used. It is also desirable that the outer joint is tape sealed in order to make the outer joint water tight.
A base portion may be attached to the side and end sheets, such that the cover extends over the entire surface of the support. The base portion may be a single sheet or more preferably an open box-like structure.
One or more internal straps may be fixed within the cover, in order to secure the support within the cover. Each strap may be fixed at one end to an inner surface of the cover, using conventional techniques such as rivetting, gluing or stitching. Preferably, stitching is used. The internal straps may be attached to their external components by joining the internal strap, base cover and external strap, preferably by stitching. Alternatively, the external strap may be joined only to the base cover. The external straps may have attachment means fitted to a free end, said attachment means being securable to a support.
One or more handles may also be formed on the external surface of the cover, preferably on opposing side or end sheets. The handles may become integral with, or attached to internal straps. This may be done by joining the handles and internal straps and the cover, by any suitable method such as glueing or stitching.
In both aspects of the present invention, the top sheet, side sheets, end sheets, outer skirt and base portion may all be of dimensions to fit a desired support. Preferably, the top sheets, side sheets, end sheets and outer skirt are all elongate pieces of stretchable material.
Preferably, the length of the top sheet along its attachment length in its laid flat state is greater than the length of the support, and a width between the attachment to the side sheets substantially equal to the width of the support.
The side sheets in their unstretched condition may be substantially equal in length to the length of the support and shorter than the length of the top sheet, with a maximum width substantially equal to the depth of the support. Preferably, the width is less than the depth of the support, and more preferably substantially equal to half the depth of the support.
The end sheets may be substantially equal in length to the length of the ends of the support, and a maximum width substantially equal to the depth of the support. The width may be less than the depth of the support, and preferably is approximately equal to half the depth of the support.
The side sheets and end sheets may be formed from a single sheet of material, having a length substantially equal to the circumference of the support and a maximum width substantially equal to the depth of the support, and preferably approximately equal to half the depth of the support.
The outer skirt may be formed from one or more pieces of material, preferably a single piece of stretchable material of a length substantially equal to the circumference of the support, and a width sufficient to cover any joint between the side sheets and base portion extending around the circumference of the support. Preferably, the width is substantially equal to the depth of the support.
The base portion may be formed form a single sheet, or may be box like in shape, having dimensions to closely fit the lower part of a support.
The cover of the present invention may be made from any suitable material, which is preferably stretchable and waterproof.